1. Field of the Invention
This invention relates to a signal reception period detector suitable for a wireless receiver.
2. Description of the Related Art
Technology that can suppress interference affecting a received signal is becoming more important in the wireless communications systems in order to efficiently use the limited frequency resources.
Use of an interference canceller that removes interference signals from a received signal is being considered as a measure to improve frequency utilization efficiency. When using a signal processing technology, for example, a successive signal separation technology, so as to remove interference signals included in a received signal, a signal reception time period of a signal component in the received signal needs to be detected and a replica is subtracted from the received signal in the signal reception time period, thereby suppressing the interference affecting the other signal components (see non-patent document 1).
Although a method of interference canceling that uses the maximum likelihood estimation (see non-patent document 2) or the minimum mean square error method (see non-patent document 3) can be used, when reception timing of the signal component included in the received signal is unknown, a sufficient effect is not demonstrated. Therefore, it is important to recognize the reception time period of each signal component.
Methods of detecting the reception time periods of the signal components in the received signal include a method based on correlation detection (see non-patent document 4, for example). According to this method, a correlation value is calculated by multiplying the received signal by a symbol sequence prescribed by a receiver and a transmitter, and a peak in the correlation value found as a result of the calculation is detected, thereby enabling detection of a reception start time of the signal, as shown in FIG. 1.
[Non-patent document 1] “V-BLAST: An Architecture for Realizing Very High Data Rates Over the Rich-Scattering Wireless Channel” Proc. ISSSE 98, September 1998.
[Non-patent document 2] “Interference Canceling Equalizer (ICE) for Mobile Radio Communications”, IEEE Trans. Vehicular Technology, November 1997.
[Non-patent document 3] “An efficient square-root algorithm for BLAST”, International conference on Acoustics, Speech, and Signal Processing (ICASSP), July 2000.
[Non-patent document 4] “State of the art digital mobile communications”, supervised Keiji Tachikawa, Kagaku Newspaper Publishing, p. 162, January 2002.
[Non-patent document 5] “Independent Component Analysis”, John Wiley & Sons, Inc., 2001.
However, there are the following disadvantages in the aforementioned related art technologies.
Regarding the timing detection method based on the correlation detection, when the length of a prescribed symbol sequence is large enough, the reception timing of the signal component can be easily detected. However, both the transmitter and the receiver have to share the prescribed symbol sequence in the method, and the correlation detection cannot be successfully performed when the transmitter and the receiver cannot cooperatively process a signal, which is, for example, sent from a different system with a different symbol sequence.
In addition, when the interference signal has a significant influence on the received signal, the symbol sequence has to be long enough to detect the correlation peak, which reduces the efficiency of spectrum usage. Additionally, if the symbol sequence used is not sufficiently long, it becomes extremely difficult to detect the reception timing of the signal component.
The present invention has been made in view of the above and may eliminate at least one of the above disadvantages. Namely, the present invention provides a signal reception period detector that is capable of detecting a reception time period for each signal component even when plural signals whose parameters are unknown are received concurrently.